This is an issue that started up for me a couple months ago. I used to be able to browse through my published images in the Library module and Lightroom would not flag them to be republished. I used to have to make an actual change to the file or the meta data in order for Lightroom to trigger a re-publish. However now it seems all I have to do is view an image in Lightroom Library module for the re-publish to be flagged. Im not changing any meta data, nor am I going into the Develop module.

Any idea what is causing this? Its getting super annoying to have to republish all these photos after simply showing them to a friend.

There have been a number of reports of this in the last few months. Please add details of your issue and your me-too vote to this topic in the official Adobe feedback forum: Lightroom: Images unexpectedly appear under "Modified Photos to Re-Publish" | Photoshop Family Customer Community. (Don't just link to this post -- Adobe won't read it and it will have less influence.) Be sure to include your exact version of LR and Windows (do Help > System Info to get the exact version). Your opinion and vote will make it more likely Adobe might investigate, and you'll get notified when the status of the bug changes.